1. Field of the Invention
The present invention relates generally to pulse compression methods and, in particular, to a method which utilizes binary sequences for maximum sidelobe suppression in a pulse compression radar system or the like.
2. Description of the Prior Art
Pulse compression involves the transmission of a long coded pulse and the processing of the received echo to obtain a relatively narrow pulse. The increased detection capability of a long pulse radar system is achieved while retaining the range resolution capability of a narrow pulse system.
Several distinct advantages are obtained utilizing pulse compression radar systems. For example, transmission of long pulses permits a more efficient use of the average power capability of the radar system. The average power of the radar system may be increased without increasing the pulse repetition frequency and, hence, decreasing the radar system's unambiguous range. Further, pulse compression radar systems are less vulnerable to interfering signals that differ from the coded transmitted signal. The use of long pulses also provides an increased system resolving capability.
A problem that has limited the utility of pulse compression and correlation receivers in radar systems has been the existence of temporal/range sidelobes in the correlation function of the radar waveform. These sidelobes allow out-of range gate returns, such as clutter, to compete with a target in a particular range gate.
A number of research efforts have addressed this problem in the past and several waveform designs have resulted in the potential reduction or elimination of the range sidelobe problem.
For example, in pulse compression radar systems, the Barker code (also known as perfect binary words) is one of the most commonly used Binary phase coded waveforms, because it has a relatively high ratio between its mainlobe and sidelobes. However, the length of the Barker code is relatively short with the maximum length of the Barker code being thirteen binary bits for a minimum sidelobe peak of one.
Several properties of binary coded waveforms are desirable if they are to be used in implementing pulse compression in pulse compression radar and tracking systems such as the target sensor component of a missile or a fire control system. These properties include very low or zero temporal sidelobes in the correlation function and very low or zero cross-correlation with other binary codes that may be implemented in sensors deployed nearby. These properties would ensure that there would be little or no degradation in sensor system performance due to out of range gate clutter returns, multiple target sidelobes or from mutual interference between deployed sensors using different codes.